Liquid crystal displays are commonly used as display devices for compact electronic apparatuses, not only because they provide good quality images but also because they are very thin. Liquid crystal in a liquid crystal display does not emit any light itself. The liquid crystal requires a light source so as to be able to clearly and sharply display text and images. Therefore, a typical liquid crystal display requires an accompanying backlight module.
Referring to FIG. 7, a typical backlight module 100 includes a light guide plate 120, a light source 110, and a reflector 130, arranged in that order from right to left as shown. The backlight module 100 further includes a plastic frame 140 for accommodating the light guide plate 120, the light source 110, and the reflector 130.
Referring also to FIG. 8, the light source 110 is interposed between the light guide plate 120 and the reflector 130, and includes a plurality of linearly arranged LED units 111. Each LED unit 111 includes a red LED 112, two green LEDs 113, and a blue LED 114, arranged in that order from top to bottom as shown. Each LED 112, 113, 114 can emit light beams of the one respective kind of primary color.
In operation of the backlight module 100, because each LED 112, 113, 114 emits one respective kind of colored light beams, a mixing process of the light beams of different colors occurs. The mixing process generally occurs in a space ranging from where the light beams emit from the LEDs 112, 113, 114 to where the light beams reach the light guide plate 120. Thereby, white light beams enter the light guide plate 120.
An optical performance of the mixed light beams reaching the light guide plate 120 is generally affected by an arrangement of the LEDs 112, 113, 114. The LEDs 112, 113, 114 are arranged along a straight line. Each pair of a red LED 112 and an adjacent blue LED 114 are located adjacent to and between two corresponding pairs of green LEDs 113. That is, in each LED unit 111, a center (not labeled) of the red LED 112 is distanced differently from the two green LEDs 113, and a center of the blue LED 114 is distanced differently from the two green LEDs 113. As a result, the light beams emitted from the LEDs 112, 113, 114 may be non-uniformly mixed, and the mixed light beams reaching the light guide plate 120 are therefore liable to be a little yellow or blue instead of being pure white. This may result in an uneven color balance of light output by the backlight module 100.
What is needed, therefore, is a backlight module that can circumvent, overcome or at least mitigate the above-described difficulties. What is also needed is a liquid crystal display including the backlight module.